Thg1 polymerases contain an additional region of conservation C-terminal to the core palm domain that comprise of 5 helices and two strands [1]. This region has several well-conserved charged residues including a basic residue found towards the end of the first helix of this unit might contribute to the Thg1-specific active site [1]. This C-terminal module of Thg1 is predicted to form a helical bundle that functions equivalently to the fingers of the other nucleic acid polymerases, probably in interacting with the template HtRNA [1]. Source: Pfam

The Thg1 protein from Saccharomyces cerevisiae is responsible for adding a GMP residue to the 5' end of tRNA His [1]. The catalytic domain Thg1 contains a RRM (ferredoxin) fold palm domain, just like the viral RNA-dependent RNA polymerases, reverse transcriptases, family A and B DNA polymerases, adenylyl cyclases, diguanylate cyclases (GGDEF domain) and the predicted polymerase of the CRISPR system [2]. Thg1 possesses an active site with three acidic residues that chelate Mg++ cations [2]. Thg1 catalyzes polymerization similar to the 5'-3' polymerases [2][3]. Source: Pfam